Intermolecular forces

Intermolecular forces

Forces between molecules or ions.

Ionic compounds

- Forces between the positive and negative

- Ionic forces are present in ionic compounds

Covalent compounds

Have no charges but can have what type of forces (2) and bonds (1)?

1. Dispersion forces

2. Dipole-dipole forces

3. H-Bonds (hydrogen bonds)

Polar molecules have what type of intermolecular forces?

dipole-dipole

Non-polar molecules have what type of intermolecular forces?

Dispersion forces

Polar ? are stronger than ?

Polar molecules are stronger than dipole dipole intermolecular forces

Types of intermolecular forces

1. Dispersion

2. Dipole-dipole

3. H- Bonds (hydrogen)

Dipole-dipole attraction

Forces of attraction between polar molecules as a result of the dipole moment within each molecule

Hydrogen bond

1. the dipole-dipole attraction between polar molecules containing these three types of polar bonds (fluorine, oxygen or nitrogen)

2. Stronger than dipole-dipole

Hydrogen bonds are stronger than

dipole-dipole

H20 Bond forces

1. dipole- dipole (the dipole-dipole attractions between polar molecules containing hydrogen and (N, O or F)

2. Hydrogen bond - a hydrogen bond is a dipole dipole attraction

3. Dispersion

London dispersion factors

- Forces that exist between nonpolar molecules and also between noble gas molecules

- Electrons are in motion around the nucleus so an even distribution is not true all the time.

- Atoms can develop an instantaneous dipolar arrangement of charge. This instantaneous dipole can induce a similar dipole in a nearby atom

- Interaction is weak and short-lived

The strength of London dispersion depends on

- Strength of attractions depend on the molar mass of the substance.

- Larger size means more electrons are available to form dipoles

Dispersion forces are weaker than

dipole dipole

List in order of least strongest to stongest...

Dispersion

Dipole Dipole

H-bonds

Dispersion < Dipole-Dipole < H-bond

Dispersion forces are present in

Non polar molecules

ex. CO2, CH4, Noble gases (have dispersion forces between atoms when come together, don't make compounds)

Hydrogen bonds are between molecules of H and

Between H and N,O, or F

ex. H20, NH3, HF

start to share electrons

Dipole-Dipole are formed between

Polar molecules

ex. H20, HCL

Ionic compounds have what type of forces?

Ionic forces

Covalent compounds have what type of forces?

1. Dispersion

2. Dipole-dipole

3. H Bonds

Dispersion

Non- polar

Induced dipole formation

Dipole-Dipole

Polar

H Bonds and between

Hydrogen and N,O, F

Physical properties

1. Boiling point

2. Density

3. Melting point

4. Viscosity

5. Solubility

Stronger intermolecular forces have higher

1. Higher boiling point

2. Higher melting point

3. Greater viscosity (related to interaction between layers of molecules)

Dispersion factors are stronger and weaker when?

1. Stronger for higher molar mass (atomic #)

- As the number of electrons increases = more distortion and dispersion

2. Weaker dispersion forces with branching (surface area increased)

All hydrocarbons are

non polar

even though structures look non symmetrical they only have dispersion forces

ex. Isobutane C4H10

What has a higher boiling point n-butane or Isobutane?

N-butane because it is not branched

Solubility

"like dissolves like"

A polar compound dissolves ?

A polar compound dissolves another POLAR COMPOUND better than a nonpolar

Benzene (C6H6) dissolves better in H20 or CCl4

CCl4 because it is nonpolar like Benzene

Alcohol are

polar (all have O + H)

HCN

Will not do more than three bonds

Intermolecular forces of HCN

Dipole - Dipole primarily

No hydrogen bond because hydrogen is bonded to carbon

Will HCN be soluble in water

yes because water is polar

Nuclear charge is greater in He or H?

He > H

He is bond more tightly closer, average distance a little less

Force of attraction in Helium is more than hydrogen

Atomic radius is greater in He and H

Atomic radius is greater in hydrogen than in helium

In the periodic table from left to right the valence shell will be the

same

In the periodic table atomic radius

Decreases from left to right (due to increasing nuclear charge)

Increases as you go down the periodic table (increasing electrons) though nuclear charge is increasing valence shell distance is already greater.

Electronegativity

a chemical property that describes the tendency of an atom to attract a shared pair of electrons

Electronegativity trend in periodic table

1. Electronegativity increases as you go from left to right, attracts more strongly

2. Electronegativity decreases as you go down a period

Ionization energy

The energy required to remove an electron from an atom, an ion, or a molecule

Minimum energy needed to remove a valence electron from a neutal atom

Electronegativity

The relative attraction that an atom has for a pair of shared electrons in a covalent bond

Ionization energy trends in periodic table

Increases from left to right more difficult to remove an electron going towards noble gas configuration

Ionization energy decreases going down table adding more shells

Metallic characteristics in periodic table

Metallic characteristics decreases from left to right

Metallic characteristics increases as you go down (Fr best metal)

Metals make positive charges more easily

Place in increasing order of atomic radius

P,N, S, AL

N > S > P > AL

Go by shell

Ionization energy increasing order

C, Be, Ca, Sr, B, Kr

Sr > Ca > Be > B > C > Kr